In order to continuously improve speeds of computer chips and optical communication, conversion of electrical connections, which have used electrical wiring between chips or between substrates to date, into optical connections by conducting light wiring therebetween is recognized to be a very important problem. Thus, a flexible film optical waveguide, which is bendable, is receiving attention for use in light wiring to realize the optical connections, and thorough research thereon is being conducted.
Methods of fabricating such a flexible film optical waveguide using a polymer are already known. In this regard, U.S. Pat. No. 6,091,874 discloses a method of fabricating a flexible film optical waveguide from polyamide and polyimide through a photolithographic process. In addition, a method of fabricating a flexible film optical waveguide from a d-PMMA polymer material through photolithography has been reported in U.S. Pat. No. 6,496,624 and the IEEE Journal of Selected Topics in Quantum Electronics, 5[5], pp 1237-1242 (1999). In the above-reported flexible film optical waveguide fabrication method, a lower cladding layer is provided on a substrate, and a core layer is then formed on the lower cladding layer. Subsequently, a photoresist layer is formed on the core layer, exposed, and developed, to form a photoresist pattern. Using the resultant photoresist pattern, the core layer is etched and patterned. Thereafter, an upper cladding layer is formed on the patterned core layer, thereby completing an optical waveguide, which is then separated from the substrate. However, the conventional flexible film optical waveguide fabricated using a polymer material through photolithography suffers because the process is complicated, includes multiple steps, is not reliable, and entails high fabrication costs. As well, the conventional polymer flexible film optical waveguide is difficult to fabricate on a mass production, due to the low thermal stability of the polymer material.
In addition, U.S. Pat. No. 6,144,795 discloses a method of forming a single-mode optical waveguide on a silicon substrate using a sol-gel organic-inorganic hybrid material through micro embossing and stamping. However, the above patent is disadvantageous because the sol-gel organic-inorganic hybrid material is used, and thus the optical waveguide is limitedly formed only on the silicon substrate. Further, the use of the above material results in low heat resistance, high color dispersion and high light loss, and causes many problems when fabricating a multi-mode optical waveguide having a large core layer, and is thus unsuitable for the fabrication of a single- and multi-mode flexible film optical waveguide.